With the progress of molecular biology, many genetic techniques have been developed, and many disease genes have been isolated and identified by these techniques. As a result, molecular biological techniques have also been incorporated in the field of medicine for the purpose of diagnosis or examination, so that it is now possible to perform types of diagnosis that had previously been extremely difficult, and the number of days necessary for examinations is being greatly reduced.
Such progress owes a lot to the practical application of the polymerase chain reaction (PCR) process in particular. The PCR process is capable of amplifying a nucleic acid in a solution in a sequence-specific manner. For example, it can indirectly prove the presence of a virus that exists only in an extremely minute amount in blood serum by amplifying and detecting a nucleic acid derived from that virus. The PCR process, however, has several problems when used for routine examinations in a clinical setting. Particularly, in preliminary processing where a nucleic acid is extracted from a biological sample, it is important to extract a highly purified nucleic acid in the purification step in order to maintain accuracy throughout the subsequent PCR process. Specifically, when extracting a nucleic acid from a biological sample in preliminary processing, the purification step must be carried out such that the nucleic acid can be separated in a pure form, with impurities eliminated to as great an extent as possible. For the purification of nucleic acids, several techniques have been proposed, as will be described below.
JP Patent Publication (Kokai) No. 11-266864 A (1999) discloses a method of automating the extraction of nucleic acids using a nucleic acid capturing tip in which a silica-containing solid phase is placed. In this technique, a nozzle tip is mounted on a movable liquid suction/discharge nozzle, and a binding accelerating agent for accelerating the binding of nucleic acid to the solid phase is sucked from a bottle. Then a nucleic acid-containing sample is sucked from a specimen container and a mixture solution of the binding accelerating agent and the sample is discharged into a reaction container. The nozzle tip is then discarded, and a nucleic acid capturing tip is newly mounted on the liquid suction/discharge movable nozzle. The mixture solution is sucked from the reaction container into the nucleic acid capturing tip. Then, the nucleic acid in the mixture solution that has been sucked from the reaction container is bound to the solid phase in the nucleic acid capturing tip, followed by discharge of the liquid in the nucleic acid capturing tip. Thereafter, the washing liquid in the washing container is sucked into the nucleic acid capturing tip and then discharged, such that the solid phase to which the nucleic acid is bound and the inside of the nucleic acid capturing tip are washed. Lastly, an eluent is sucked into the nucleic acid capturing tip, and then the eluent containing the nucleic acid separated from the solid phase is discharged into a purified product container. In this manner, a nucleic acid can be purified from a nucleic acid-containing sample.
Thus in the method disclosed in JP Patent Publication (Kokai) No. 11-266864 (1999), the solid phase to which nucleic acid is bound and the inside of the nucleic acid capturing tip are washed by sucking washing liquid from the washing container into the tip and then discharging it therefrom in a repeated manner. It takes more time for suction than for discharge due to the resistance of the solid phase, so that the method has a very poor washing efficiency and a significantly lowered throughput. Furthermore, should the washing liquid remain on the solid phase or the inside walls of the nucleic acid capturing tip, this would affect the concentration of the eluent and could possibly lower the nucleic acid purification performance.
Further, in the case of washing with a plurality of kinds of washing reagents, they are dispensed via the same flow path. As a result, interference is caused between one washing reagent and another upon switchover, which causes a reduction in concentration or dispensing accuracy, thereby possibly resulting in a lowered washing efficiency.
It is therefore the object of the invention to provide a sample processing device and method whereby a solution, such as a washing liquid, can be put through a separation column, such as a nozzle tip having a solid phase, quickly and reliably, so that an improved throughput can be achieved.